A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section.
The compressor section may include low, intermediate and high pressure compressors, and the turbine section can include low, intermediate and high pressure turbines. The high pressure turbine drives the high pressure compressor through an outer shaft to form a high spool. The intermediate turbine drives an intermediate compressor and forms an intermediate spool and the low pressure turbine drives the low pressure compressor through an inner shaft to form a low spool.
The fan section may also be driven by the low spool. In a direct drive gas turbine engine includes a fan section driven by the low spool such that the low pressure compressor, low pressure turbine and fan section rotate at a common speed in a common direction. In some 3-spool gas turbine configurations, the low pressure compressor is driven by the intermediate turbine and the low pressure turbine is utilized only to drive the fan section. The separation of the low pressure compressor form the low pressure turbine provides for rotation at different more efficient speeds.
A speed reduction device such as an epicyclical gear assembly may be utilized to drive the fan section such that the fan section may rotate at a speed different than the turbine section so as to increase the overall propulsive efficiency of the engine. In such engine architectures, a shaft driven by one of the turbine sections provides an input to the epicyclical gear assembly that drives the fan section at a reduced speed such that both the turbine section and the fan section can rotate at closer to optimal speeds.
Although geared architectures have improved propulsive efficiency, turbine engine manufacturers continue to seek further improvements to engine performance including improvements to thermal, transfer and propulsive efficiencies.